These data choreograph the nocturnal dance of mothers and babies- -the dance McKenna had predicted--but with mutual promptings and responses. It’s not that mothers regulate their babies’ breathing. The sleepers are, instead, physiologically entwined; the movements and breathing of each partner affect the other. When one arouses, the other often wakes up a bit, too.
McKenna proposes that transient arousals are especially important because they give babies practice in waking up. All babies experience apneas, or pauses in breathing, several times a night. If a pause becomes prolonged, a healthy baby will wake up to breathe. Many researchers believe that SIDS babies have some deficiency that inhibits their arousal. When they stop breathing, they’re less apt to wake up--and thus more likely to die. But if aroused more often by a parent, McKenna reasons, they may learn better how to do it on their own, and wake up one night when it really matters.
McKenna also suggests that co-sleeping helps a baby master breathing techniques. During sleep, just as during wakefulness, adults shift through periods of controlled or automatic breathing, switching between neocortical-driven breaths and brain stem-operated breaths. Babies undergo that flip-flop each time they wake up. When sleeping with Mom, a baby reacts to her movements and wakes up more times during the night--an average of 24 percent more, McKenna finds, than when sleeping alone--thus getting more practice in the repeated hop from one kind of breathing to the other. Sleep has evolved against these interruptions, says McKenna, and they may serve as practice for the baby when it has more serious internally based interruptions in breathing.
Such fitful sleep may, in fact, be the norm for adults as well. The mothers in McKenna’s experiments passed through transient arousals 60 percent more frequently when sleeping with their babies than when sleeping alone. We Westerners have the ‘die’ theory of sleep, McKenna says, laughing. You close your eyes, fall asleep, and basically die--you become totally unconscious until you wake up in the morning--and you hope for the best. If there’s anything in between, there’s something wrong with you. Other people in the world don’t sleep like that. The !Kung bushmen, for example, get up, tend the fire, talk, then go back to sleep. Western culture has streamlined what we think is normal. And if people can’t conform, there’s a disease out there for them--it’s called insomnia. A small group of sleep researchers have also admitted that humans are not monophasic sleepers--they are biphasic. The afternoon nap is biologically based.
His point is that cultures dictate norms unrelated to what might or might not be evolutionarily natural--that is, bred into human physiology. He feels that the extreme American emphasis on individualism, and the view that husband and wife have a relationship apart from the children, have reinforced notions that infants are born too dependent and should sleep by themselves as soon as possible. In contrast, Japanese infants normally sleep with their parents. This, too, is a culturally bound notion, but instead of opting for independence, the Japanese foster interdependence. Interestingly enough, the rate of SIDS is significantly lower in Japan than in the United States: less than one per 1,000 births.
Data for immigrant populations in the United States suggest that such cultural differences may indeed play a role. For example, Chinese immigrants in California have an incidence of SIDS 38 times higher than nonimmigrant Chinese in Hong Kong. Among other Asian-American populations the SIDS rates vary, but the rate increases the longer a group has lived in the United States. The Vietnamese, for example, arrived later than the Japanese, and their SIDS rate is lower. McKenna feels that the pattern may be explained by immigrants’ adopting the American style of placing babies in their own beds. His speculation cannot be confirmed, of course, until other possible influences--such as changes in feeding practices--are ruled out.
McKenna began giving talks about his ideas in the early eighties. Then, in 1986, he published a massive paper on his work, which attracted a lot of attention. So far the response from the medical community has not been as critical as McKenna first feared. Marian Willinger, who directs SIDS research at the National Institute of Child Health and Human Development, says, In general this is a new area for infant and child health--tying parenting styles with physiology--and therefore McKenna and Mosko’s basic research is important for all babies.
One medical researcher was deeply impressed. I think their work is terrific, says Jeffrey Laitman, an anatomist at New York’s Mount Sinai School of Medicine. His own research on the development of the throat and voice box in infants supports Mc-Kenna’s hunch that SIDS is linked to the evolution of speech making. In newborns, as in many animals, the larynx locks into the back of the nasal cavity, Laitman explains. This enables them to breathe and swallow at roughly the same time. But in humans the larynx begins to drop down into the throat in the first few months of life. No other mammal goes through such a tremendous metamorphosis, and there’s a great possibility of miscues--as well as a far greater ability to make the wide range of sounds used in talking.
But McKenna’s not just out to prevent SIDS; his approach has always been more anthropological than medical. His larger goal is to show that early sleeping practices are important to everyone’s health. This past January he and Mosko brought the first of 30 mother-baby pairs, including 15 co-sleepers, into the lab to investigate whether the sleep and breathing patterns of the co-sleeping babies are different from those of the babies who habitually sleep alone. McKenna expects to finish this study by the end of the year, but even then he’ll be a long way from proving that co- sleeping is best for everyone in the long run. His argument that it seems to work well in traditional cultures cuts two ways. After all, most American babies, with their background of solitary sleeping, also grow up apparently healthy.
For now, McKenna aims to prove that co-sleeping is natural and normal for the average baby, a reasonable option rather than a dangerous, misguided practice that should be discouraged, as stated in current advice books. Should a parent or parents feel good about co-sleeping, elect it as a favored strategy, and it is done responsibly, he writes, nothing could be better for their infant or child.
He is also philosophical about his potential role as a revolutionary in American parenting styles. There is nothing profound about what I am trying to document or argue for--it’s based on evolutionary history. It doesn’t take any genius to know there may be some naturalistic interactions between co-sleeping babies and mothers, or babies and caretakers. Like those who have discovered in the twentieth century that breast-feeding is good for babies, I spend all my time documenting the obvious.
Medical Research On...
Each year hundreds of papers are published on SIDS, pointing the finger at a host of possible culprits. Mothers who smoke during pregnancy, for example, have been told they’re upping their baby’s risk of SIDS about threefold. Babies may also be at higher risk if they are born prematurely or of low birth weight, as a sibling rather than a firstborn, or to a young mother. Babies who lie on their stomach have a higher risk; more babies die of SIDS in winter; elevated body temperature from a stuffy room or overdressing may be a factor.
Still, none of this explains the actual cause of sudden death. Risk factors are simply things that may make a baby more vulnerable, explains Marian Willinger, who directs SIDS research for the National Institute of Child Health and Human Development. Just because cigarette smoking is linked with an increased risk doesn’t mean that cigarette smoking causes SIDS. A lot of SIDS babies’ mothers don’t smoke. There’s something about the baby itself that predisposes it to SIDS.
Pinning down that something, however, has so far proved impossible. At this point, explains Willinger, SIDS is a diagnosis of exclusion. If you can’t find any other cause of death after a full postmortem, then it’s called SIDS--so by definition we’re starting without much to help us.
Nevertheless, some strides have been made. The most popular theory is that something is wrong with the way vulnerable babies arouse themselves from sleep--they’re supposed to wake up when they stop breathing for an unusual length of time, but they don’t. To investigate this idea, neurophysiologist Ron Harper and his colleagues at UCLA checked the records of nearly 7,000 babies whose heartbeats and breathing were recorded in a British study. Sixteen of those babies later died of SIDS; Harper found that they had gone through far fewer short respiratory pauses while sleeping than the ones who were still alive. Although the reason for this difference is not yet known, it is a true disparity.
Other researchers are looking at where respiration is controlled- -in the brain. The brains of all newborns are still developing; for instance, the neurons are not all covered by their protective sheaths of myelin. Early last year Hannah Kinney of Children’s Hospital in Boston and her colleagues showed that myelination in the brains of 61 infants who died of SIDS lagged significantly behind myelination in 89 children who died of other causes--though again this is so far just a clue.
Of course, a disease with such a nebulous definition can easily fool you. Researchers are fairly certain that 3 to 10 percent of SIDS cases are actually the result of inborn metabolic defects. And a study published last summer showed that a few babies diagnosed as succumbing to SIDS--fewer than 1 percent--might have suffocated on soft bedding such as beanbag cushions.
Yet researchers do feel that SIDS is a discrete entity with its own physiological mechanism, not just a conglomeration of other syndromes that simply need to be teased apart. The scientists really believe that after all is said and done there will be a core of babies with a certain characteristic abnormality that makes them vulnerable to sudden death, says Willinger. We won’t keep peeling away layers of onion until there is nothing left. -Lori Oliwenstein